Messages in this thread Patch in this message | | | Date | Thu, 06 May 2021 21:34:05 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 13/13] jump_label,x86: Allow short NOPs |
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Now that objtool is able to rewrite jump_label instructions, have the compiler emit a JMP, such that it can decide on the optimal encoding, and set jump_entry::key bit1 to indicate that objtool should rewrite the instruction to a matching NOP.
For x86_64-allyesconfig this gives:
jl\ NOP JMP short: 22997 124 long: 30874 90
IOW, we save (22997+124) * 3 bytes of kernel text in hotpaths.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/include/asm/jump_label.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
--- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -28,6 +28,22 @@ _ASM_PTR "%c0 + %c1 - .\n\t" \ ".popsection \n\t" +#ifdef CONFIG_STACK_VALIDATION + +static __always_inline bool arch_static_branch(struct static_key *key, bool branch) +{ + asm_volatile_goto("1:" + "jmp %l[l_yes] # objtool NOPs this \n\t" + JUMP_TABLE_ENTRY + : : "i" (key), "i" (2 | branch) : : l_yes); + + return false; +l_yes: + return true; +} + +#else + static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch) { asm_volatile_goto("1:" @@ -40,6 +56,8 @@ static __always_inline bool arch_static_ return true; } +#endif /* STACK_VALIDATION */ + static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch) { asm_volatile_goto("1:"
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